Contactless signal testing

ABSTRACT

A method for performing contactless signal testing includes receiving, with a testing pad of an integrated circuit, a signal within an electron beam, converting an electrical current created by the e-beam to a voltage with a number of diodes connected to a positive voltage supply, extracting a digital test signal from the voltage signal with a digital inverter, and passing the test signal to digital circuitry within the integrated circuit.

BACKGROUND

Integrated circuits include multiple intricate components that must betested for compliance with design specifications. This is often done byapplying a test signal to the digital circuitry within the integratedcircuit to make sure that the circuitry performs as desired. The testsignal is typically applied to a bonding pad on the integrated circuit.

Bonding pads are used to connect an integrated circuit to externaldevices and circuits. Thus, the bonding pads provide a conductive pathto the digital circuitry within the integrated circuit. Bonding pads maybe sensitive to damage from external probes. Thus, the probes used toapply the testing signal can potentially damage the bonding pads,thereby making the circuit unusable.

Damaged bonding pads can be especially wasteful with integrated circuitsthat include multiple wafers stacked on top of each other. For example,some three dimensional circuit technology involves bonding multiplecircuits formed on separate wafers to each other. With suchtechnologies, the circuit on each wafer is tested individually before itis bonded to another wafer. Thus, if the bonding pads are damaged duringthe testing, only that wafer can be discarded rather than the entirestack of wafers. But, a final test is still done when all wafers havebeen bonded to each other. If the bonding pad on the stack of wafers isdamaged during testing, the entire stack of wafers may have to bediscarded. Accordingly, it would be desirable to have a testing methodthat would involve less risk of damaging the bonding pads of anintegrated circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 is a diagram showing an illustrative integrated circuit allowingfor contactless testing, according to one example of principlesdescribed herein.

FIG. 2 is a diagram showing illustrative signals associated withcontactless testing, according to one example of principles describedherein.

FIG. 3 is a diagram showing an illustrative integrated circuit allowingfor contactless testing with multiple channels, according to one exampleof principles described herein.

FIG. 4 is a diagram showing an illustrative integrated circuit allowingfor contactless testing and separate bonding pads, according to oneexample of principles described herein.

FIG. 5 is a diagram showing an illustrative integrated circuit allowingfor contactless testing with a time division multiplexed signal,according to one example of principles described herein.

FIG. 6 is a diagram showing an illustrative integrated circuit allowingfor contactless testing using optics, according to one example ofprinciples described herein.

FIG. 7 is a flowchart showing an illustrative method for contactlesstesting, according to one example of principles described herein.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the disclosure. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Moreover,the performance of a first process before a second process in thedescription that follows may include embodiments in which the secondprocess is performed immediately after the first process, and may alsoinclude embodiments in which additional processes may be performedbetween the first and second processes. Various features may bearbitrarily drawn in different scales for the sake of simplicity andclarity. Furthermore, the formation of a first feature over or on asecond feature in the description that follows may include embodimentsin which the first and second features are formed in direct contact, andmay also include embodiments in which additional features may be formedbetween the first and second features, such that the first and secondfeatures may not be in direct contact.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. For example, if the device in the figures is turned over,elements described as being “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the exemplary term “below” can encompass both an orientation ofabove and below. The apparatus may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein may likewise be interpreted accordingly.

FIG. 1 is a diagram showing an illustrative integrated circuit allowingfor contactless testing. According to the present example, thecontactless testing system 100 includes a transmitter 102 that transmitsan electron beam 104 to a testing pad 106. The testing pad 106 isconnected to a current-to-voltage converter 124 that may include anumber of diodes 110. Based on the voltage created at thecurrent-to-voltage converter 124, a digital inverter 112 can be used tooutput either a digital high or digital low signal. The inverter 112 isthen connected to digital circuitry 114 within the integrated circuit116 to be tested.

The electron beam 104 is produced by an electron beam transmitter 104.The transmitter 102 can be placed near the testing pad 106 but not makeactual contact with the testing pad 106. Thus, the electrons within theelectron beam 104 are projected to the testing pad 106. The electronbeam 104 can be turned on an off to embed a digital signal within theelectron beam 104. The rate at which the electron beam 104 is turned onand off can be adjusted in order to project the digital test signal atthe desired frequency.

The testing pad 106 may be an electrically conductive pad designed toreceive the electrons from the electron beam 104. Because there is nophysical contact between the transmitter 102 and the testing pad 106,the testing pad 106 does not have to be large enough to allow for astrong flow of electricity across a physical contact. In some examples,the size of the testing pad 106 may be within a range of about 0.80-1.20square micrometers.

After the electrons from the electron beam 104 reach the testing pad106, they will flow to a node 120 through a first diode 124. From thatnode 120, the electrons will flow through a number of diodes 110 thatare connected between the node 120 and a positive voltage supply, V_(DD)(122). Integrated circuits typically include a positive voltage supplyline 122 and a negative voltage supply line that are used for thevarious digital components within the integrated circuit. Becauseelectrons will flow towards a positive voltage, they will be drawntowards the positive voltage supply 122.

The flow of electrons across the diodes 110 will produce an electriccurrent 118 in the opposite direction. This electric current will, inturn, change a voltage level at the node. If that voltage level is highenough, it will trip the inverter 112 so that the output of the inverter112 will be a digital high signal instead of a digital low signal. Adigital inverter 112 is a digital circuit component that produces a highsignal when the input is a low signal. Conversely, the inverter 112produces a high signal when the input is a low signal.

The input required to trip the inverter 112 may be based on the designspecifications of the inverter 112. Likewise, the amount of currentrequired to produce the desired voltage needed to trip the inverter 112may be based on design specifications of the diodes 110. In general, alarger number of diodes 110 will make it so that less current isrequired to trip the inverter 112. But, a larger number of diodes 110may take up more space on the integrated circuit 116. A design with alarger number of diodes 110 may be more problematic in cases where thereare hundreds or thousands of independent testing pads 106 on anintegrated circuit 116.

The output of the digital inverter 112 represents the original signalembedded within the electron beam 104. Thus, the digital circuitry 114can be provided with the testing signal without using a probe to makephysical contact with the testing pad 106. This reduces the risk ofdamage to an integrated circuit 116.

FIG. 2 is a diagram showing illustrative signals associated withcontactless testing. FIG. 2 illustrates three different signals. Thefirst signal 206 represents the signal embedded in the electron beam.The second signal 212 represents the electric current flowing throughthe diodes (110, FIG. 1). The third signal 222 represents the signaloutput of the inverter (112, FIG. 1).

The first signal 206 is represented along a graph 200 wherein thehorizontal axis 204 represents time and the vertical axis 202 representselectron flow. The first signal 206 represents a basic clock signal thatconsistently alternates between a digital high and a digital low. Thissignal can be produced by turning the electron beam on and off.Specifically, when the electron beam is on, the signal 206 is at a highpoint 208. Conversely, when the electron beam is off, the signal is atthe low point.

The second signal 212 is represented along a graph 210 wherein thehorizontal axis 204 represents time and the vertical axis 214 representselectric current. The second signal 212 appears as a saw-tooth signal.The ramp up portions 216 of the second signal 212 correspond to the highpoints 208 of the first signal 206. Specifically, when the electron beamis on, the electric current flowing through the diodes that areconnected to the testing pad will begin to increase. When the electronbeam is turned off, the current level in the diodes will sharply dropback down to zero.

The third signal 222 is represented along a graph 220 wherein thehorizontal axis 204 represents time and the vertical axis representsvoltage 224. The third signal 222 resembles the first signal 206.Specifically, when the electron beam is on in the first signal, theoutput of the digital inverter is at a high point 226. Conversely, whenthe electron beam is off, the third signal is at a low point 228.

The third signal 222 may not precisely correspond to the first signal206. This is because there may be propagation delays and other factors.For example, the electric current will have to ramp up to a certainlevel before the voltage at the node (120, FIG. 1) is high enough totrip the inverter so that the inverter produces a different output.

FIG. 3 is a diagram showing an illustrative integrated circuit 312allowing for contactless testing with multiple channels. According tothe present example, an integrated circuit may include multiplechannels, each channel corresponding to one testing pad. Digitalcircuitry 310 is often designed to operate with several signal paths ata time. In some integrated circuits there may be hundreds or eventhousands of signal paths. Each of these channels should be tested toensure that the integrated circuit works as designed.

According to the present example, a number of transmitters 302 arearranged to be in alignment with a number of testing pads 306 on theintegrated circuit 312. The transmitters each produce an independentlycontrolled electron beam 304. Thus, each of the electron beams 304 mayhave a different signal embedded therein. This corresponds to realoperating conditions of the integrated circuit 312.

After each of the different signals is received by the correspondingtesting pads 306, receivers 308 are used to extract the testing signaland send the testing signal to the corresponding digital circuitry 310.A receiver 308 includes the current-to-voltage component as describedabove. Specifically, the current-to-voltage component may be a diodestack connected between the testing pad 306 and a positive voltagesupply.

FIG. 4 is a diagram showing an illustrative integrated circuit 402allowing for contactless testing and separate bonding pads 408. Asdescribed above, a bonding pad 408 and a testing pad 406 may be the samething. In some cases, however, the bonding pad 408 may be separate fromthe testing pad 406. But, the testing pad 406 is still connected to thesame signal path 412 as the bonding pad 408.

By separating the testing pads 406 from the bonding pads 408, fewertesting pads 406 may be used because one testing pad may connect tomultiple bonding pads. In such a system, a multiplexer is used to encodethe signal before it is transmitted to the testing pad. A de-multiplexeris then used to de-multiplex the signal and transmit each individualsignal to its respective signal path.

FIG. 5 is a diagram showing an illustrative integrated circuit allowingfor contactless testing with a time division multiplexed signal.According to the present example, the electron beam 502 is configured totransmit a time division multiplexed signal 504 to the testing pad 516.The receiver 510 then transmits the recovered signal to a temporarystorage device 512. From there, the signal is de-multiplexed by ade-multiplexer 518 before it is transmitted to the digital circuitry 508of the integrated circuit 506.

Time division multiplexing works by transmitting multiple signals withinvarious time slots of the main signal. For example, to multiplex foursignals into one signal, the main signal is divided into four repeatingtime slots. During the first time slot, a portion of the first signal isinserted. During the second time slot, a portion of the second signal isinserted. During the third time slot, a portion of the third signal isinserted. Finally, during the fourth time slot, a portion of the fourthsignal is inserted. This process is repeated continually duringtransmission of the signal.

After the main signal is received by the receiver 510, it is passed tothe de-multiplexer 518. The de-multiplexer 518 includes a memorycomponent 512 for temporary storage. The memory component 512 acts as abuffer to hold the received data until it can be de-multiplexed by thede-multiplexer 514. In one example, the memory component 512 includes anumber of registers. The number of registers may match the number oftime slots within the main multiplexed signal. The data stored withinthe time slots of the main multiplexed signal may be put into eachregister as it comes in. Specifically, the data within the first timeslot may be put in a first register. The data within the second timeslot may be put within the second register. The data within the thirdtime slot may be put within the third register. Finally, the data withinthe fourth time slot may be put within the fourth register.

The de-multiplexer 518 also includes a de-compressor 514. After theregisters are full and there is enough data for each of the time slots,the data can be moved to the de-compressor 514 for time decompression.When data is time-division multiplexed, it may be compressed into a morecompact format before it is transmitted. The de-compressor 514 willappropriately decompress the data so that it is ready for transmissionto the digital circuitry 508.

While the example of FIG. 5 shows a time division multiplexed signalwith four channels being embedded into a main signal, other embodimentsmay have more signals embedded within a main signal. For example, anintegrated circuit may have 1000 bonding pads and 20 testing pads. Eachtesting pad may have 50 different signals multiplexed within using timedivision multiplexing. Thus, the total number of signals is 1000, whichmatches the number of bonding pads.

FIG. 6 is a diagram showing an illustrative integrated circuit allowingfor contactless testing using optics. According to the present example,the optical contactless testing system 600 includes a light transmitter602 to produce an optical beam 604. The optical beam may have a signalembedded therein. The optical beam 604 is received by a testing pad 606that includes a number of photo-sensitive diodes 608. Thephoto-sensitive diodes 608 are connected to a node 612 at an input of adigital inverter 614. The output of the digital inverter 614 isconnected to digital circuitry 616 within the integrated circuit 618.

The optical transmitter 602 may project a signal in a manner similar tothe electron beam transmitter (102, FIG. 1). By turning the optical beam604 on and off, the optical beam can be used to transmit a signal to thetesting pad 606. The testing pad 606 includes a number ofphoto-sensitive diodes 608 configured to receive the optical beam.

Photo-sensitive diodes convert energy in the form of photons toelectrical energy. Specifically, the photons that imping on the activeregions of the photo-sensitive diodes 608 push electrons from thevalence band into the conduction band, thus causing the flow ofelectricity. The electrons will flow toward the positive voltage supply620, thus causing an electric current 610 to flow away from the positivevoltage supply 620. This will change the voltage at node 612. Thischange in voltage will trip the inverter to produce a high or lowsignal. Thus, the signal embedded within the optical beam is extractedand provided to the digital circuitry 616.

FIG. 7 is a flowchart showing an illustrative method for contactlesstesting, according to one example of principles described herein.According to certain illustrative examples, the method 700 includes astep for receiving 702, with a testing pad of an integrated circuit, asignal within an electron beam. The method 700 further includes a stepfor converting 704 an electrical current created by the e-beam to avoltage with a number of diodes connected to a positive voltage supply.The method 700 further includes a step for extracting 706 a digital testsignal from the voltage signal with a digital inverter. The method 700further includes a step for passing 708 the test signal to digitalcircuitry within the integrated circuit.

According to certain illustrative examples, a method for performingcontactless signal testing includes receiving, with a testing pad of anintegrated circuit, a signal within an electron beam. The method furtherincludes converting, with a number of diodes connected to a positivevoltage supply, an electrical current signal created by the electronbeam to a voltage signal. The method further includes extracting, with adigital inverter, a test signal from the voltage signal and passing thetest signal to digital circuitry within the integrated circuit.

According to certain illustrative examples, an integrated circuit devicehaving contactless testing capability includes a testing pad to receivean electron beam having a signal embedded therein, a number of diodesconnected between the testing pad and a positive voltage supply, thediodes to convert an electric current induced by the electron beam to avoltage, a digital circuit component to extract a digital test signalfrom the signal based on a voltage level of the number of diodes.

According to certain illustrative examples, an integrated circuit devicehaving contactless testing capability includes a testing pad comprisinga number of photo-sensitive devices that produce an electric current inresponse to an optical beam, a current-to-voltage structure to convertthe electric current from the photo-sensitive devices to a voltage, anda digital circuit component to extract a digital test signal embedded inthe optical beam based on a voltage level output by thecurrent-to-voltage structure.

It is understood that various different combinations of the above-listedembodiments and steps can be used in various sequences or in parallel,and there is no particular step that is critical or required.Additionally, although the term “electrode” is used herein, it will berecognized that the term includes the concept of an “electrode contact.”Furthermore, features illustrated and discussed above with respect tosome embodiments can be combined with features illustrated and discussedabove with respect to other embodiments. Accordingly, all suchmodifications are intended to be included within the scope of thisinvention.

The foregoing has outlined features of several embodiments. Those ofordinary skill in the art should appreciate that they may readily usethe present disclosure as a basis for designing or modifying otherprocesses and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those of ordinary skill in the art should also realize that suchequivalent constructions do not depart from the spirit and scope of thepresent disclosure, and that they may make various changes,substitutions and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A method for performing contactless signaltesting, the method comprising: receiving, with a testing pad of anintegrated circuit, a signal within an electron beam; converting, with anumber of diodes connected to a positive voltage supply, an electricalcurrent signal created by the electron beam to a voltage signal, whereinthe number of diodes includes a diode stack of multiple diodes;extracting, with a digital inverter, a test signal from the voltagesignal; and passing the test signal to digital circuitry within theintegrated circuit.
 2. The method of claim 1, wherein a frequency of thesignal is set by an on and off period of the electron beam.
 3. Themethod of claim 1, wherein the number of diodes in the diode stack ofmultiple diodes is within a range of 3-6.
 4. The method of claim 1,wherein the testing pad corresponds to a bonding pad.
 5. The method ofclaim 1, further comprising, with a number of additional testing pads onthe integrated circuit, receiving a number of additional independentsignals.
 6. The method of claim 5, wherein a total number of testingpads on the integrated circuit is less than a total number of bondingpads.
 7. The method of claim 1, wherein the test signal is atime-division multiplexed signal.
 8. The method of claim 7, furthercomprising, temporarily storing the time-division multiplexed signal ina memory of the integrated circuit.
 9. The method of claim 8, furthercomprising, de-multiplexing the multiplexed signal with ade-multiplexing circuit of the integrated circuit before passing thetest signal to the digital circuitry.
 10. The method of claim 1, whereinthe testing pad is within a size range of about 0.80-1.20 squaremicrometers.
 11. An integrated circuit device having contactless testingcapability, the integrated circuit comprising: a testing pad to receivean electron beam having a signal embedded therein; a number of diodesconnected between the testing pad and a positive voltage supply, thediodes to convert an electric current induced by the electron beam to avoltage, wherein the number of diodes includes a diode stack of multiplediodes; and a digital circuit component to extract a digital test signalfrom the signal based on a voltage level of the number of diodes. 12.The integrated circuit device of claim 11, wherein the testing pad isalso a bonding pad.
 13. The integrated circuit device of claim 11,wherein the testing pad is separate from a bonding pad and the testingpad and bonding pad connect to the same circuit path within theintegrated circuit.
 14. The integrated circuit device of claim 11,wherein the number of diodes in the diode stack having a number ofdiodes within a range of 3 and
 6. 15. The integrated circuit device ofclaim 11, further comprising additional testing pads, each of theadditional testing pads corresponding to one of a multiple of bondingpads.
 16. The integrated circuit device of claim 11, further comprising:a memory to temporarily store a time-division multiplexed signal; and ade-multiplexer to de-multiplex a signal stored in the memory.
 17. Theintegrated circuit device of claim 11, wherein the testing pad is withina size range of about 0.80-1.20 square micrometers.
 18. An integratedcircuit device having contactless testing capability, the integratedcircuit comprising: a testing pad comprising a number of photo-sensitivedevices that produce an electric current in response to an optical beam;a current-to-voltage structure to convert the electric current from thephoto-sensitive devices to a voltage, the current-to-voltage structurecomprising a diode stack of multiple diodes; and a digital circuitcomponent to extract a digital test signal embedded in the optical beambased on a voltage level output by the current-to-voltage structure. 19.The integrated circuit device of claim 18, wherein the testing padcorresponds to a bonding pad of the integrated circuit.
 20. Theintegrated circuit device of claim 18, further comprising: a memory totemporarily store a time-division multiplexed signal embedded within theoptical beam; and a de-multiplexer to de-multiplex the time-divisionmultiplexed signal stored in the memory.